Comparing diving behaviour among three Procellaria petrels and implications for bycatch mitigation

<p><strong>A major threat to seabirds globally is incidental capture in fisheries. Of threats to seabirds, incidental capture (hereafter bycatch) has the largest scope and severity, impacting 30% of seabird species. When foraging, many seabirds dive to utilise marine resources, allowing them to access baited hooks deployed by longline fishing vessels. Developing bycatch mitigation methods requires an understanding of seabird foraging behaviour. However, foraging behaviour is highly variable within and among species and may be influenced by an array of biotic and abiotic factors. Thus, we must foremost understand foraging behaviour in its ecological context. In my first chapter, I explore the diving behaviour of three Procellaria petrels, all of which are vulnerable to bycatch in longline fisheries. I deployed time-depth recorders (TDR) and geolocation sensor (GLS) loggers on Westland (Procellaria westlandica), White-chinned (P. aequinoctialis) and Black Petrels (P. parkinsoni). With this data I examine changes in diving behaviour across the breeding period, identify diurnal and nocturnal habits, and investigate sex-specific behaviours. My findings reveal significant differences in diving behaviour among and within species. Black Petrels dived deeper on average (5.93 m) than Westland (2.26 m) and White-chinned Petrels (2.63 m), and performed the deepest dive recorded for the Procellaria genus (38.5 m). Westland Petrels were the faster divers, with a mean dive descent rate of 1 m/s. Westland and Black Petrels exerted greater diving effort when rearing chicks than when incubating eggs. Westland Petrels dived throughout day and night, with a preference for nocturnal diving, while Black Petrels dived almost exclusively during the day. These insights enable me to make specific bycatch mitigation recommendations for the three species, which align with recent recommendations by the Agreement on the Conservation of Albatrosses and Petrels (ACAP), thus promoting efforts for trans-boundary changes in fishing practices. In my second chapter I develop a method to diving behaviour associated with fisheries activities with deployments of TDR and Global Positioning System (GPS) loggers. A key limitation of diving behaviour studies attempting to inform mitigation measures is that seabirds may exhibit different diving behaviours when around fishing vessels. The ability to distinguish between natural and fishing-associated foraging opens doors for future studies to look at fine-scale changes in diving behaviour around fishing vessels. This will enable us to further fine-tune bycatch mitigation measures. Overall, this thesis provides invaluable insights into the foraging ecology of Procellaria petrels, with significant implications for their conservation.</strong></p>